1. Field of the Invention
The present invention relates to signal demodulation and decoding and more particularly to the extraction of a single signal or channel from a set of frequency division multiplexed signals or channels. The invention further relates to a high speed half-band filter having a dynamically resettable center frequency for extracting a single preselected frequency band from a broader band input signal.
2. Related Technical Art
There are many operational situations in the communications and signal processing arts in which it is desirable to separate, extract, or monitor a small sample or single channel of a large number of Frequency Division Multiplexed (FDM) signals. Such signals are typically used in satellite or other advanced communication systems, such as fiber-optics or waveguide-based communication systems. This multiplexing allows many signals to be combined into a single wideband channel to make maximum use of channel capacity, high transfer rates, common central processing, etc.
The task of separating particular communication signals from a FDM packet or group of signals is a complex and difficult task, especially at the high speeds typically involved. It is necessary to adequately isolate the single channel and extract it from adjacent channels before any decoding, verification, or other processing can occur. There is a variety of full FDM/TDM demultiplexers available which are designed to perform the extraction task.
Current demultiplexers achieve adequate extraction results but with a great deal of complexity, expense, and power consumption. These demultiplexers are also typically designed to achieve high accuracy tracking and information decoding. Currently such demultiplexers employ a finite-impulse-response (FIR) filter (or fast convolution equivalent) as the only type of filter that performs phase distortionless linear signal filtering. However, to achieve a high level of signal resolution or accuracy, a very high order filter (either one very long filter or many small filters) is required which also increases the complexity and cost, while decreasing throughput speed. Unfortunately, for many advanced applications, especially where equipment is to be mobile or otherwise power limited, complexity and speed become critical design issues.
What is needed is an apparatus or method of operation that can reduce the complexity and power requirements for high speed FDM signal extraction. In addition, it would be advantageous if the apparatus is capable of good channel separation. A signal demultiplexer embodying these improvements would have increased applicability over current designs for many situations.